Why Move to 64 Bits? Memory
The main reason it will be worth moving everyone to 64 bits eventually is memory: 32-bit Windows editions top out at about 3GB of system memory. Even if it's theoretically possible for them to address the full 4GB, or even some more than that, as a practical matter it causes compatibility conflicts with certain device drivers, and the decision was made to limit desktop Windows and the cheaper editions of Windows Server. I won't go into the pluses and minuses of this decision, significant though they may be. The fact is that, to get more than about 3.1GB to 3.5GB of usable RAM in a Windows desktop edition, you need to use the 64-bit version. Already we're at the point with Vista where 2GB to 2.5GB is considered the sweet spot, and there's no reason to build a system with less; memory is that cheap (2GB of Crucial PC5400 667MHz DDR2 at TigerDirect today: $39.99 after rebate). No system I build or recommend from now on will have less than 2GB.I asked Microsoft for comment on this column and got some boilerplate from them:
It's also likely that 64-bit versions will be demonstrably faster, even for common desktop scenarios before too long, both for the access to larger blocks of memory and for the optimizations that will come from the larger registers and larger numbers of registers.
The 64-bit editions of Windows Vista-on PCs with at least 4GB of memory-can be more responsive when running many programs simultaneously, are highly compatible with the hardware devices and software programs you use today, and are ready for the next generation of 64-bit-optimized programs, which promise dramatic performance and experience improvements.Microsoft has taken the opportunity with the 64-bit editions to introduce new security-related features and to make mandatory some security features that were optional in 32-bit Windows:
- More Responsive When Multitasking-With 64-bit editions of Windows Vista and at least 4GB of memory, your PC can provide a smoother, more responsive experience when running many programs simultaneously.
- Highly Compatible with Devices and Programs-You will find that most of the hardware devices and software programs you use today will work properly with 64-bit editions of Windows Vista.
- Ready for 64-Bit-Optimized Programs-With 64-bit editions of Windows Vista and at least 4GB of memory, you're ready for the next generation of 64-bit-optimized programs that will use large amounts of memory to deliver dramatic performance gains and innovative new experiences.
- DEP is turned on for all 64-bit processes on 64-bit Windows and cannot be turned off.
- 64-bit Vista introduced Kernel Patch Protection (PatchGuard), which stops even kernel-mode programs from using unsupported mechanisms to modify key kernel data structures. This feature caused a big stir among security software vendors who use such undocumented features to implement host intrusion prevention.
- Kernel mode programs in 64-bit Windows Vista (and, I assume, Windows Server 2008 and all future Windows versions) must be digitally signed with a key based on a code signing certificate issued by a trusted certificate authority.